Heretofore, cited as a light emitting type electronic display device has been an electroluminescence display (ELD). Constituting elements of ELD include an inorganic electroluminescence element and an organic electroluminescence element (hereinafter also referred to as an organic EL element).
The organic EL element is constituted in such a manner that a light emitting layer, which incorporates light emitting compounds, is sandwiched between a cathode and an anode. In the above element, electrons and positive holes are injected into the light emitting layer and are subjected to recombination, whereby exciton is generated. During deactivation of the resulting exciton, light (fluorescence and phosphorescence) is emitted. Light emission can be realized via application of a voltage of several V—several tens V. Further, the organic EL element exhibits a wide viewing angle due to the self-light emitting type, and high visibility, whereby in view of space saving and portability, it has attracted attention.
For example, an EL element is known in which a thin organic film is formed via deposition of organic compounds (for example, Applied Physics Letters, p. 913-(1987)). The organic EL element described in the above reference incorporates a laminated layer structure of electron transporting materials and positive hole transporting materials, whereby it realizes significant enhancement of light emission characteristics compared to conventional monolayer type elements. The above laminated layer type element is formed via deposition of low molecular weight organic materials as an element material.
Further disclosed is a technique in which an element is formed via deposition of organic molecules having a repeated unit of at most 10 which are prepared by polymerization of compounds having a polymerizable group (refer, for example, to Patent Document 1). Still further disclosed is a technique in which a first layer is formed via polymerization of compounds having a polymerizable group, and subsequently a second layer is formed thereon via polymerization of compounds having a polymerizable group (refer, for example, to Patent Document 1).
However, such forming methods employing deposition display major problems such as poor utilization efficiency of materials, an increase in space, and the insufficient accuracy during the production process of the elements.
Nature, 397 (1999) 121 describes that π electron conjugation based polymers such as polyparaphenylene vinylene (PPV), and derivatives thereof, may be employed as a light emitting material. Some of these have been employed as a clock backlight. These polymer based materials capable of being subjected to film formation via a casting method exhibit not only advantages in the production process but also advantages in excellent durability compared to low molecular weight light emitting materials. However, organic polymer materials when employed via a coating method, exhibit disadvantages such as low solubility in solvents and low light emission efficiency. In order to overcome these drawbacks, a method is available in which a polymer precursor is employed and polymers are formed after coating to become insoluble, whereby elution is minimized. As the above example, it is possible to cite a method proposed by Cambridge Display Technology Co. in which PPV is employed as a precursor. The above method is detailed on pages 73—of Organic Electro-Luminescent Materials and Devices, 1997. However, since in this method, polymer structures are limited, it is not possible to apply it to various compounds to form a light emitting element.
Further, another method is available in which after casting employing monomers, elution is minimized in such a manner that the monomers are polymerized to become insoluble (refer, for example, to Patent Documents 3 and 4). By employing the above methods, it becomes possible to employ a laminated layer structure, whereby light emitting efficiency is improved. However, problems have still remained in which due to insufficient enhancement of the light emitting efficiency, dark spots tend to occur, and the life of the element is not long enough due to distortion of the boundary.
Patent Document 1: Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP-A) No. 5-247547
Patent Document 2: JP-A No. 2004-103401
Patent Document 3: JP-A No. 2003-73666
Patent Document 4: JP-A No. 2003-86377